Facet extraction LED and method for manufacturing the same

ABSTRACT

A facet extraction LED improved in light extraction efficiency and a manufacturing method thereof. A substrate is provided. A light emitting part includes an n-type semiconductor layer, an active layer and a p-type semiconductor layer sequentially stacked on the substrate. A p-electrode and an n-electrode are connected to the p-type semiconductor layer and the n-type semiconductor layer, respectively. The p- and n-electrodes are formed on the same side of the LED. The light emitting part is structured as a ring.

CLAIM OF PRIORITY

This application claims the benefit of Korean Patent Application No.2006-15274 filed on Feb. 16, 2006 in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting diode, and moreparticularly, to a facet extraction light emitting diode (LED) having ahigh light emitting efficiency, and a manufacturing method thereof.

2. Description of the Related Art

Recently, a light emitting diode (LED) utilizing a group III-V or groupII-VI compound semiconductor material is largely used in a lightemitting device for producing visible light. Also, such an LED isadopted for a light source of various products such as lighteningboards, lightening devices, and LCD backlights. In a method tomanufacture the semiconductor LED, an n-type semiconductor layer, anactive layer and a p-type semiconductor layer are sequentially grown ona substrate to form a light emitting structure.

The typical semiconductor LED is structured to extract light from upperor lower surfaces but not a plane surface, i.e., a facet. However, theLED cannot exceed 15% in its light extraction efficiency without aseparate technique such as photonic crystal, which, even if adopted,yields merely about 30% light extraction efficiency. Such low lightextraction efficiency is attributed to light absorption in a crystal andlight loss at an electrode as well.

As an alternative structure, a facet extraction LED has been proposed.The facet extraction LED is structured to extract light from a facetwhere the active layer is exposed. Here, a plurality of the facetextraction LED can be arranged to manufacture a smaller surface lightsource device. The facet extraction LED may be configured as a SeparateConfinement Heterostructure (SCH) to trap light around the active layer.Yet, in the facet extraction LED, a light extraction face is smallerthan other faces and thus travels a long distance in a crystal beforebeing extracted. This increases light loss in the crystal and reduceslight extraction amount, thereby lowering light extraction efficiency to2% or less.

FIG. 1 is a perspective view illustrating a conventional facetextraction LED. Referring to FIG. 1, the facet extraction LED 10includes an n-type semiconductor 13, an active layer 15 and a p-typesemiconductor layer 17 sequentially formed on a conductive substrate 11.The n- and p-type semiconductor layers 13 and 17, and the active layer15 constitute a light emitting structure. A p-electrode 18 is formed onthe p-type semiconductor layer 17 and an n-electrode 19 is formedunderneath the conductive substrate 11.

As shown in FIG. 1, light is extracted and emitted from a facet A wherethe active layer 15 is exposed. The facet A, if the greater amount oflight is extracted therefrom than from other faces, serves as a lightextraction face. However, the facet A for extracting light is smallerthan other faces such as an facet B, upper or lower surface. That is, awidth W of the light extraction face A along a plane direction of theactive layer is smaller than a distance L between the light extractionface A and its opposing face. This causes light to propagate a longerdistance in a crystal before being extracted outside the LED, therebyresulting in considerable light loss in the crystal.

After all, the conventional facet extraction LED 10 fails to assuresufficient light extraction efficiency or light emitting efficiency.Further, the surface light source device such as the LCD backlightmanufactured using a plurality of the facet extraction LED suitablyserves to miniaturize a product, however, without exhibiting sufficientbrightness due to degraded efficiency of the LED 10. This as a resultcalls for the facet extraction LED improved in lightextraction-efficiency more significantly.

SUMMARY OF THE INVENTION

The present invention has been made to solve the foregoing problems ofthe prior art and therefore an aspect of the present invention is toprovide a facet extraction light emitting diode (LED) having lightextraction efficiency.

Another aspect of the invention is to provide a facet extraction LEDimproved in light extraction efficiency, and a manufacturing methodthereof.

According to an aspect of the invention, the facet extraction LEDincludes a substrate; a light emitting part including an n-typesemiconductor layer, an active layer and a p-type semiconductor layersequentially stacked on the substrate; and a p-electrode and ann-electrode connected to the p-type semiconductor layer and the n-typesemiconductor layer, respectively, the p- and n-electrodes formed on thesame side of the LED, wherein the light emitting part comprises a ringstructure. The ring structure has outer and inner facets crossing theactive layer, the outer facet extracting a greater amount of light thanthe inner facet.

According to an embodiment of the invention, each of the n-typesemiconductor layer, the active layer and the p-type semiconductor layercomprises a group III-V compound semiconductor material. For example,the semiconductor layers are made of a group III nitride-basedsemiconductor such as GaN.

According to a preferred embodiment of the invention, the light emittingdiode further comprises an anti-reflection film formed on the outerfacet of the ring structure. Preferably, the anti-reflection film has areflectivity ranging from 0% to 5% with respect to light from the activelayer.

According to another preferred embodiment of the invention, the facetextraction LED further includes a reflective film formed on an innerfacet of the ring structure. Preferably, the reflective film has areflectivity ranging from 90% to 100% with respect to light from theactive layer. Preferably, the facet extraction LED includes both theanti-reflection film and the reflective film.

According to another embodiment of the invention, the ring structure hasa circular outline. According to further another embodiment of theinvention, the ring structure has a polygonal outline such as a hexagonor an octagon.

According to further another embodiment of the invention, the facetextraction LED comprises a flip-chip LED. Here, the p- and n-electrodesare bonded onto a submount for mounting the LED, e.g., a reflective cupof a package, by solder bumps.

The ring structure satisfies a following relationship:

5≦W/L≦10,000,

where L is a distance between the outer and inner facets, and W is anouter peripheral length of the active layer on the outer facet.Preferably, the distance L between the outer and inner facets of thering structure ranges from 1 μm to 100 μm.

According to further another embodiment of the invention, the ringstructure has protrusions and indentations on the outer facet. The outerfacet with protrusions and indentations further enhances lightextraction efficiency therefrom.

According to further another embodiment of the invention, the substratecomprises a sapphire substrate. According to further another embodimentof the invention, the substrate comprises a conductive substrate. Forexample, the conductive substrate is a GaN substrate or a SiC substrate.

According to further another preferred embodiment of the invention, then-electrode is surrounded by the ring structure. Specifically, then-electrode is disposed on the n-type semiconductor layer, surrounded bythe ring structure. In a case where the substrate is a conductivesubstrate, the substrate comprises a conductive substrate, and then-electrode surrounded by the ring structure is in direct contact withthe substrate.

According to further another embodiment of the invention, the outer andinner facets of the ring structure are inclined with respect to astacking direction of the semiconductor layers in such a fashion that adistance between the outer and inner facets increases toward thesubstrate.

According to further another embodiment of the invention, the n- andp-type semiconductor layers and the active layer comprise a separateconfinement heterostructure. This SCH structure traps light around theactive layer, reducing light loss at the electrodes.

According to another aspect of the invention, the method formanufacturing the facet extraction LED includes:

sequentially forming an n-type semiconductor layer, an active layer anda p-type semiconductor layer on a substrate;

forming a p-electrode with a ring pattern on the p-type semiconductorlayer;

selectively etching the p-type semiconductor layer, the active layer andthe n-type semiconductor layer to form a light emitting part of a ringstructure under the p-electrode; and

forming an n-electrode to be surrounded by the light emitting part.

According to an embodiment of the invention, the step of forming thelight emitting part of the ring structure includes partially etching aportion of the n-type semiconductor layer, in a thickness direction, insuch a fashion that a remaining portion of the etched n-typesemiconductor layer portion is surrounded by the light emitting part.

According to further another embodiment of the invention, the substratecomprises a conductive substrate, and the step of forming the lightemitting part of the ring structure includes entirely etching a portionof the n-type semiconductor layer, in a thickness direction, so that theportion of the n-type semiconductor layer is completely removed in aregion surrounded by the light emitting part. Here, the n-electrodesurrounded by the light emitting part is in direct contact with thesubstrate.

According to a preferred embodiment of the invention, the manufacturingmethod further includes forming an anti-reflection film on the outerfacet of the ring structure. Also, the manufacturing method furtherincludes forming a reflective film reflective film on the inner facet ofthe ring structure.

In this specification, ‘a group III nitride semiconductor’ designates abinary, ternary or quaternary compound semiconductor having acomposition expressed by Al_(x)Ga_(y)In_((1-x-y))N, where 0≦x≦1, 0≦y≦1,and 0≦x+y≦1.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a perspective view illustrating a conventional facetextraction LED;

FIG. 2 is a perspective view illustrating a facet extraction LEDaccording to a first embodiment of the invention;

FIG. 3 is a plan view illustrating the facet extraction LED of FIG. 2;

FIG. 4 is a side cross-sectional view illustrating a facet extractionLED cut along the line XX′ of FIG. 3;

FIG. 5 is a partial plan view for explaining decrease in totalreflection of the facet extraction LED shown in FIG. 2;

FIG. 6 is a plan view illustrating a facet extraction LED according to asecond embodiment of the invention;

FIG. 7 is a side cross-sectional view illustrating a facet extractionLED according to a third embodiment of the invention;

FIG. 8 is a perspective view illustrating a facet extraction LEDaccording to a fourth embodiment of the invention;

FIG. 9 is a side cross-sectional view illustrating a facet extractionLED according to a fifth embodiment of the invention;

FIG. 10 illustrates a facet extraction LED mounted in a reflective cupof a package according to an embodiment of the invention;

FIG. 11 illustrates a facet extraction LED mounted in a reflective cupof a package according to another embodiment of the invention;

FIG. 12 is an energy band diagram illustrating a facet extraction LEDaccording to further another embodiment of the invention;

FIG. 13 is a side cross-sectional view for explaining a method formanufacturing a facet extraction LED according to an embodiment of theinvention; and

FIG. 14 is a side cross-sectional view for explaining a method formanufacturing a facet extraction LED according to another embodiment ofthe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Exemplary embodiments of the present invention will now be described indetail with reference to the accompanying drawings, in which preferredembodiments of the invention are shown. The invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.

First Embodiment

FIG. 2 is a perspective view illustrating a facet extraction lightemitting diode (LED) according to a first embodiment of the invention.FIG. 3 is a plan view illustrating the facet extraction LED of FIG. 2.FIG. 4 is a side cross-sectional view cut along the line XX′ of FIG. 3.

Referring to FIGS. 2 to 4, the facet extraction LED 100 includes ann-type semiconductor layer 103, an active layer 105 and a p-typesemiconductor layer 107 sequentially grown on a substrate 101. Thesemiconductor layers 103, 105, and 107 may be made of a group IIInitride semiconductor such as GaN. The substrate 101 may be a sapphiresubstrate or a conductive substrate of e.g. GaN and SiC. A p-electrode109 is formed on the p-type semiconductor layer 107. The p-electrode 109is not illustrated in FIGS. 2 and 3 for convenience's sake. The n- andp-type semiconductor layers 103 and 107 and the active layer areprotruded from the substrate 101 to constitute a light emitting part150.

As shown in FIGS. 2 to 4, the light emitting part 150 of the LED 100features a ring structure. Especially, in this embodiment, the lightemitting part 150 is structured as a circular ring. An n-electrode 110is surrounded by the light emitting part 150 of the ring structure andformed on the n-type semiconductor layer 103. The p- and n-electrodes109 and 110 of the LED 100 are formed to face the same direction, thatis, formed on the same side of the LED 100. Accordingly the LED 100 isof a planar or lateral-electrode type.

An outer facet C of the ring-structured light emitting part 150 extractsthe greatest amount of light out of facets. The outer facet C of thelight emitting part 150 is larger than an inner facet D thereof, andthus serves as a major light extraction face. That is, light extractionamount from the outer facet C of the light emitting part 150 is greaterthan that from the inner facet D thereof. This allows light generatedfrom the active layer 105 to be chiefly extracted from the outer facet C(see FIG. 2). An anti-reflective film 120 is formed on the outer facet Cby coating in order to further enhance light extraction efficiency.Also, a reflective film 130 is formed by coating on the inner facet Dopposing the outer facet C, i.e., the major light extraction face tosuppress light from being radiated from the inner facet D.

Referring to FIGS. 2 to 4, an outer peripheral length W (correspondingto the circumference of a dotted circle in FIG. 4) of the active layeron the outer facet, i.e., is bigger than a distance L between the outerfacet C and its opposing face D. (compare with FIG. 1). In this fashion,the outer peripheral length W greater than the distance L enables themajor light extraction face, i.e., outer facet C to be larger in sizethan the other facet D. This allows light to be extracted from thelarger facet. Furthermore, due to the distance L smaller than the outerperipheral length W, light generated from the active layer 105propagates a shorter distance in a crystal before being extracted fromthe outer facet C to the outside. This as a result diminishes multiplereflection and light loss in the crystal, thereby remarkably boostinglight extraction efficiency and brightness.

To sufficiently shorten a light path in the crystal, a ratio of theouter peripheral length W to the distance L is preferably at least 5.For example, the outer peripheral length W is about 2500 μm and thedistance L is about 50 μm. However, the distance L too smaller than theouter peripheral length W of a predetermined dimension renders theactive layer 105 smaller-sized and poses difficulty to a technicalprocess. Thus preferably, a ratio W/L of the outer peripheral length Wto the distance L is not greater than 10,000. Preferably, the ratio W/Lranges from 10 to 10,000, and more preferably, 50 to 10,000. To moreshorten the light path in the crystal, the ratio W/L may be at least100.

In order to downscale the size of the facet extraction LED 100 andenlarge the ratio W/L, preferably, the distance L is 100 μm or less.Also, to assure a sufficient area of the active layer 105, the distanceL is preferably at least 1 μm. Especially, the distance L may range from1 μm to 50 μm. Moreover, the facet extraction LED can be reduced to anultra-small size by setting the distance L in the range of 20 μm or lessor 10 μm or less.

The anti-reflection film 120 restrains light incident from inside thecrystal on the outer facet C from being reflected, thereby facilitatinglight extraction from the outer facet C. Therefore, desirably, theanti-reflection film 120 has a smaller reflectivity. Preferably, theanti-reflection film 120 has a reflectivity ranging from 0% to 5% withrespect to light from the active layer 105.

The reflective film 130 suppresses light from being extracted from theinner facet D and reflects light incident on the inner facet D towardthe outer facet C. In this embodiment, since the outer facet C is amajor light extraction face, preferably light is not extracted from theother facet D. This is why a reflective film 130 with high reflectivityis formed on the inner facet D opposing the outer facet C. Therefore,desirably, the reflective film 130 has a greater reflectivity.Preferably, the reflective film 130 has a reflectivity ranging from 90%to 100% with respect to light from the active layer 105.

Light loss occurring in the facet extraction LED 100 may result fromlight absorption and reflection in the p-electrode 109 or the substrate101. To minimize such light loss, it is preferable to trap light aroundthe active layer 105 as much as possible. To this end, desirably thesemiconductor layers 103, 105 and 107 feature a Separate ConfinementHeterostructure (SCH). This SCH structure has a stack of alow-reflectivity layer/a high-reflectivity layer/an active layer/ahigh-reflectivity layer/a low-reflectivity layer so that light can betrapped around the active layer effectively. FIG. 12 is an energy banddiagram illustrating an exemplary SCH structure. In FIG. 12, ‘Ec’denotes an edge of a conduction band and ‘Ev’ denotes an edge of avalence band.

Referring to FIG. 12, the active layer is sandwiched between p- andn-side optical waveguide layers, and the active layer and the opticalwaveguide layers are sandwiched between p- and n-type clad layers. Asshown, the active layer may feature a multiple quantum well structurehaving GaN barriers and InGaN wells stacked alternately. The p- andn-type clad layers have a lower reflectivity than the optical waveguidelayers. For example, the optical waveguide layers are made of GaN andthe p- and n-type clad layers are made of AlGaN having a lowerreflectivity and bigger band gap than GaN. The p-side optical waveguidelayer may be made of undoped GaN (u-GaN) or p-doped GaN (p-GaN). Thisenergy band structure of SCH can be employed to trap light around theactive layer 105 effectively.

According to this embodiment, the outer facet C, i.e., the major lightextraction face, is convex, thus effectively decreasing a totalreflection ratio of light incident on the light extraction face. Thisdecline in total reflection is manifested in FIG. 5.

FIG. 5 (a) is a partial plan view illustrating a light emitting part 150of a ring structure. FIG. 5( b) is a partial plan view illustrating acomparative embodiment of the light emitting part 150′ of a linearstructure. As shown in FIG. 5 (a), light traveling at an angle a withrespect to a central line Lc of the light emitting part 150 enters aconcave outer facet C at a greater angle of b (b>a). This renders thelight less likely to be total reflected on the outer facet C, thusincreasing light extraction amount from the outer facet C.

However, as shown in FIG. 5( b), in a case where the light emitting part150′ is of a linear structure, light traveling at an angle a withrespect to a central line Lc′ of the light emitting part 150′ enters afacet C′ at an angle identical to a. This does not lead to decrease intotal reflection on the facet. Moreover a plane facet D′ hardly reducestotal reflection.

Second Embodiment

FIG. 6 is a plan view illustrating a facet extraction LED 100′ accordingto a second embodiment of the invention. In this embodiment, the facetextraction LED has protrusions and indentions on a major lightextraction face. As shown in FIG. 6, a light emitting part 150 of thefacet extraction LED 100′ features a ring structure, and has protrusionsand indentions on an outer facet R of the ring structure. Theprotrusions and indentions on the outer facet R makes light incident onthe outer facet R less likely to be total reflected. This accordinglyrenders the light less likely to be extinct due to total reflection,thereby further enhancing light extraction efficiency of the LED.

Third Embodiment

FIG. 7 is a side cross-sectional view illustrating a facet extractionLED 100″ according to a third embodiment of the invention. In thisembodiment, two opposing facets of a ring-structured light emitting partare inclined. Referring to FIG. 7, an outer facet E and an inner facet Fof the light emitting part 150 are inclined with respect to a stackingdirection of semiconductor layers 103, 105 and 107. Thus, the lightemitting part 150 is widened toward a substrate 101 into across-sectional shape of a trapezoid. In this fashion, the two facets ofthe light emitting part 150 are inclined so that some portion of lightreflected from the outer and inner facets E and F propagates toward thesubstrate 101. In a case where this facet extraction LED 100″ is adoptedfor a flip chip LED, the outer and inner facets E and F can be inclinedas just described thereby to further boost light extraction amount fromthe substrate 101 and light extraction efficiency of the LED (see FIG.10).

Fourth Embodiment

FIG. 8 is a perspective view illustrating a facet extraction LED 200according to a fourth embodiment of the invention. In this embodiment, alight emitting part is shaped as a hexagon. As shown in FIG. 8, in thisembodiment, the light emitting part 250 formed on a substrate 101features a ring structure. An anti-reflective film 220 is formed on anouter facet of the ring structure and a reflective film 230 is formed onan inner facet thereof. An n-electrode 210 is surrounded by the ringstructure. However, the light emitting part 250 of the ring structure isshaped as not a circle but a hexagonal ring, unlike the aforesaidembodiment.

As shown in FIG. 8, even when the light emitting part 250 features ahexagonal ring structure instead of a circular ring structure, an outerperipheral length of the active layer on the outer facet is bigger thana distance between the outer facet, i.e., major light extraction faceand the opposing inner facet. This ensures higher light extractionefficiency than a conventional facet extraction light emitting LED. Thelight emitting part 250 is shaped as a hexagonal ring but the inventionis not limited thereto. For example, the light emitting part 250 may beconfigured as a polygonal ring structure such as an octagon or adecagon.

Fifth Embodiment

FIG. 9 is a side cross-sectional view illustrating a facet extractionLED 300 according to a fifth embodiment of the invention. In thisembodiment, an n-electrode 110 is surrounded by a light emitting part150 of a ring structure, and directly formed on a substrate 101′. Asshown in FIG. 9, the n-electrode 110 of the facet extraction LED 300 issurrounded by the ring-structured light emitting part 150 and notably indirect contact with the substrate 101′. In order to bring then-electrode 110 in direct contact with the substrate 101′, the substrate101′ is exposed when mesa-etching is performed to form the ringstructure, and the n-electrode 110 is formed on the exposed substrate100′ (see FIG. 14). The substrate 101′ needs to be conductive toelectrically connect the n-electrode 110 with the substrate 101′.

In this embodiment, an outer peripheral length W of the active layer onthe outer facet is bigger than a distance L between the outer and innerfacets C and D. This increases an area ratio of the major lightextraction face, i.e., outer facet C with respect to the other facet D,thereby causing light to propagate a short distance in a crystal. Thusas just described, this clearly assures improvement in light extractionefficiency and brightness.

In the aforesaid embodiments, the anti-reflective film 120 is formed onthe outer facet C, R and E of the ring-structured light emittingstructure 150 and the reflective film 130 is formed on the inner facet Dand F thereof. But the invention is not limited thereto. For example,either of the anti-reflective film 120 and the reflective film 130 maybe omitted. Alternatively, both of the anti-reflective film 120 and thereflective film 130 may be omitted (see reference sign 100″ of FIG. 11).

Flip-Bonded LED

FIGS. 10 and 11 illustrate a facet extraction LED mounted in areflective cup of a package according to the aforesaid embodiments.Especially in FIGS. 10 and 11, the facet extraction LED is flip-chipbonded to a submount, i.e., the reflective cup of the package in thisembodiment.

Referring to FIG. 10, electrodes of the facet extraction LED 100″ areflipped over to face a bottom surface of the reflective cup 60 of thepackage so that a substrate 101 faces a direction where light emits.Here, preferably, the substrate 101 is a transparent substrate of e.g.,sapphire or GaN. The p- and n-electrodes 109 and 110 are bonded onto alower surface of the reflective cup 60 of the package by solder bump 51and 53. In a case where the reflective cup 60 is made of a conductivematerial such as metal, an adequate insulating layer 57 is disposed onthe bottom surface of the reflective cup 60, and an electrode patternmay be formed thereon. A metal pattern 55 made of Au may be interposedbetween the solder bump 53 and the bottom surface of the reflective cup.

As shown in FIG. 10, light extracted from a major light extraction face,i.e., an outer facet of the light emitting part 150 is reflected onto aside of the reflective cup to travel upward, i.e., in a light extractiondirection. In a case where the substrate 101 is a transparent substrateof e.g., sapphire or GaN, light is extracted from the outer facet of thelight emitting part 150 and from the substrate 101 as well. Notably, asshown in FIG. 10, a distance between the outer and inner facets of thelight emitting part 150 increases toward the substrate 101 so that someportion of light reflected from the outer and inner facets can beemitted toward the substrate 101.

In FIG. 11, a facet extraction LED 100′″ is flip-chip bonded onto abottom surface of a reflective cup 60. Especially, an anti-reflectivefilm and a reflective film are not formed in the facet extraction LED100′″. Therefore, light is radiated from not only an outer facet butalso an inner facet of the ring-structured light emitting part 150. Yet,light emitted from the inner facet may be absorbed or re-reflected by abump 53 or a metal layer 55 which is centered in the package. Inconsequence, light emitted from the outer facet of the light emittingpart 150 and the substrate 101 (in case of a transparent substrate), isused as an actual output light.

Evidently, not only the facet extraction LED 100′ and 100′″ of thisembodiment but also other facet extraction LEDs 100, 100′, 200, and 300according to other embodiments can be flip-chip bonded. FIGS. 10 and 11employ the reflective cup 60 as an LED submount. But optionally, othertypes of submount may be utilized. Furthermore, the facet extraction LEDcan be mounted on the submount by a bonding method other than flip-chipbonding. For example, the LED of the invention can be mounted on thesubmount by wire bonding.

Manufacturing Method

FIG. 13 is a side cross-sectional view for explaining a method formanufacturing a facet extraction LED according an embodiment of theinvention. In this embodiment, an n-electrode is formed on an n-typesemiconductor layer.

First, referring to FIG. 13 (a), the n-type semiconductor layer 103, anactive layer 105 and a p-type semiconductor layer 107 are sequentiallyformed on an insulating or conductive substrate 101. The semiconductorlayers 103, 105 and 107 may be made of a group III GAN-based nitride.The group III nitride semiconductor layers can be grown via e.g.,Metal-Organic Chemical Vapor Deposition (MOCVD).

Next, as shown in FIG. 13 (b), a p-electrode 109 of a ring pattern isformed on the p-type semiconductor layer. The ring pattern may feature acircle (see FIG. 2) or a polygon such as a hexagon (see FIG. 8).

Subsequently, as shown in FIG. 13 (c), the p-electrode 109 or a mask(not illustrated) placed thereover is utilized as an etching mask toselectively etch the semiconductor layers 103, 105 and 107. This allowsa light emitting part 150 with a ring structure to be formed under thep-electrode 109 as shown. The ring structure of the light emitting part150 can be a circle or a polygon such as a hexagon as described above.To form the ring-structured light emitting part 150 via etching, then-type semiconductor layer 103 is partially etched in a thicknessdirection thereof. Especially, in a case where the substrate 101 is aninsulating substrate of e.g., sapphire, the n-type semiconductor layer103 should be partially etched in a thickness direction thereof in orderto be made in contact with the n-electrode.

Thereafter, as shown in FIG. 13 (d), the n-electrode 10 is surrounded bythe ring-structured light emitting part 150. The n-electrode 110 isformed on the n-type semiconductor layer 103, surrounded by the lightemitting part 150. This allows the n-electrode 110 and the n-typesemiconductor layer 103 to be electrically connected with each other.

Then, as shown in FIG. 13 (e), optionally, an anti-reflective film 120is formed on an outer facet C of the ring-structured light emitting part150 and a reflective film 130 is formed on an inner facet D thereof.This accordingly produces the facet extraction LED according to anembodiment of the invention.

FIG. 14 is a side cross-sectional view for explaining a method formanufacturing a facet extraction LED according to another embodiment ofthe invention. In this embodiment, an n-electrode is directly formed ona conductive substrate. The manufacturing method of this embodiment canbe applied to obtain the facet extraction LED 300 of FIG. 9.

First, referring to FIG. 14( a), an n-type semiconductor layer 103, anactive layer 105, and a p-type semiconductor layer 107 are sequentiallyformed on a conductive substrate 101′ of e.g., GaN. Then, as shown inFIG. 14 (b), a p-electrode of a ring pattern is formed on the p-typesemiconductor layer 107. Subsequently, as shown in FIG. 14 (c), thesemiconductor layers 103, 105, and 107 are selectively etched to form alight emitting part 150 of a ring structure under the p-electrode 109.In this embodiment, to obtain the ring structure via selective etching,the n-type semiconductor layer is entirely etched to expose theconductive substrate 101′. Here, the conductive substrate 101′ may beetched to a certain thickness.

Afterwards, as shown in FIG. 14 (d), an n-electrode 110 is surrounded bythe ring-structured light emitting part 150 and directly formed on theconductive substrate 101′. This brings the n-electrode 110 in directcontact with the conductive substrate 101′. Then, as shown in FIG. 14(e), optionally, an anti-reflective film 120 is formed on an outer facetC of the ring structure and a reflective film 130 is formed on an innerfacet D thereof. This as a result produces the facet extraction LEDhaving the n-electrode 110 in direct contact with the conductivesubstrate 101′.

As set forth above, according to exemplary embodiments of the invention,a light emitting part is shaped as a ring to increase an area ratio of amajor light extraction face. This consequently increases lightextraction amount from the light extraction face and light extractionefficiency of an entire device. In addition, this renders light lesslikely to be total reflected on the light extraction face, therebyfurther enhancing light extraction efficiency and brightness.

While the present invention has been shown and described in connectionwith the preferred embodiments, it will be apparent to those skilled inthe art that modifications and variations can be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

1. A facet extraction light emitting diode comprising: a substrate; alight emitting part including an n-type semiconductor layer, an activelayer and a p-type semiconductor layer sequentially stacked on thesubstrate; and a p-electrode and an n-electrode connected to the p-typesemiconductor layer and the n-type semiconductor layer, respectively,wherein the p- and n-electrodes are formed on the same side of thediode, wherein the light emitting part comprises a ring structure. 2.The facet extraction light emitting diode according to claim 1, whereinthe ring structure has outer and inner facets crossing the active layer,the outer facet extracting a greater amount of light than the innerfacet.
 3. The facet extraction light emitting diode according to claim1, wherein each of the n-type semiconductor layer, the active layer andthe p-type semiconductor layer comprises a group III-V compoundsemiconductor material.
 4. The facet extraction light emitting diodeaccording to claim 1, further comprising an anti-reflection film formedon the outer facet of the ring structure.
 5. The facet extraction lightemitting diode according to claim 4, wherein the anti-reflection filmhas a reflectivity ranging from 0% to 5% with respect to light from theactive layer.
 6. The facet extraction light emitting diode according toclaim 1, further comprising a reflective film formed on an inner facetof the ring structure.
 7. The facet extraction light emitting diodeaccording to claim 6, wherein the reflective film has a reflectivityranging from 90% to 100% with respect to light from the active layer. 8.The facet extraction light emitting diode according to claim 1, whereinthe ring structure has a circular outline.
 9. The facet extraction lightemitting diode according to claim 1, wherein the ring structure has apolygonal outline.
 10. The facet extraction light emitting diodeaccording to claim 1, comprising a flip-chip LED.
 11. The facetextraction light emitting diode according to claim 1, wherein the ringstructure satisfies a following relationship:5≦W/L≦10,000, where L is a distance between the outer and inner facets,and W is an outer peripheral length of the active layer on the outerfacet.
 12. The facet extraction light emitting diode according to claim1, wherein the distance between the outer and inner facets of the ringstructure ranges from 1 μm to 100 μm.
 13. The facet extraction lightemitting diode according to claim 1, wherein the ring structure hasprotrusions and indentations on the outer facet.
 14. The facetextraction light emitting diode according to claim 1, wherein thesubstrate comprises a sapphire substrate.
 15. The facet extraction lightemitting diode according to claim 1, wherein the substrate comprises aconductive substrate.
 16. The facet extraction light emitting diodeaccording to claim 1, wherein the conductive substrate comprises aGaN-based substrate.
 17. The facet extraction light emitting diodeaccording to claim 1, wherein the n-electrode is surrounded by the ringstructure.
 18. The facet extraction light emitting diode according toclaim 17, wherein the n-electrode is disposed on the n-typesemiconductor layer, surrounded by the ring structure.
 19. The facetextraction light emitting diode according to claim 17, wherein thesubstrate comprises a conductive substrate, and wherein the n-electrodesurrounded by the ring structure is in direct contact with thesubstrate.
 20. The facet extraction light emitting diode according toclaim 1, wherein the outer and inner facets of the ring structure areinclined with respect to a stacking direction of the semiconductorlayers in such a fashion that a distance between the outer and innerfacets increases toward the substrate.
 21. The facet extraction lightemitting diode according to claim 1, wherein the n- and p-typesemiconductor layers and the active layer comprise a separateconfinement heterostructure.
 22. A method for manufacturing a lightemitting diode comprising: sequentially forming an n-type semiconductorlayer, an active layer and a p-type semiconductor layer on a substrate;forming a p-electrode with a ring pattern on the p-type semiconductorlayer; selectively etching the p-type semiconductor layer, the activelayer and the n-type semiconductor layer to form a light emitting partof a ring structure under the p-electrode; and forming an n-electrode tobe surrounded by the light emitting part.
 23. The method according toclaim 22, wherein the step of forming the light emitting part of thering structure comprises partially etching a portion of the n-typesemiconductor layer, in a thickness direction, in such a fashion that aremaining portion of the etched n-type semiconductor layer portion issurrounded by the light emitting part.
 24. The method according to claim23, wherein the n-electrode is formed on the remaining portion of then-type semiconductor layer surrounded by the light-emitting part. 25.The method according to claim 22, wherein the substrate comprises aconductive substrate, and wherein the step of forming the light emittingpart of the ring structure comprises entirely etching a portion of then-type semiconductor layer, in a thickness direction, so that theportion of the n-type semiconductor layer is completely removed in aregion surrounded by the light emitting part.
 26. The method accordingto claim 25, wherein the n-electrode is surrounded by the light emittingpart and is in direct contact with the substrate.
 27. The methodaccording to claim 22, further comprising forming an anti-reflectionfilm on the outer facet of the ring structure.
 28. The method accordingto claim 22, further comprising forming a reflective film on the innerfacet of the ring structure.